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1,135,871. Natural gas liquefaction process. AIR PRODUCTS & CHEMICALS Inc. 28 June, 1966 [29 June, 1965], No. 28964/66. Heading F4P. Natural hydrocarbon gas having been freed of hexane and most of the pentane content in separators 12, 20, 34, 36 is fed at 600 p.s.i.a. through lines 50, 51 to the base of a vertical coil 52 where the residual gas is cooled to its liquefaction temperature in indirect heat exchange with successive sprays 82, 84, 86, 88 of at least four liquid refrigerants at decreasing temperatures; said liquid refrigerants being obtained by separation from a mixture thereof in a four-stage column 92 followed by expansion in valves 102, 107, 113, 119 resulting in a temperature fall prior to delivery from the spray heads 82, 84, 86, 88. The multi-component refrigerant mixture of Cl to C 6 saturated hydrocarbons and nitrogen is supplied by a compressor 94 at about 515 p.s.i.a. to the first stage 99 of column 92. Liquid C 2- C 6 hydrocarbons are expanded at 102 and issue from spray 82 whilst gaseous hydrocarbons and nitrogen are cooled in a coil 74 beneath spray 82 and fed to the second stage 104 from which liquid C 2 -C 4 hydrocarbons are withdrawn expanded at 107 and issue from spray 84 whilst gaseous hydrocarbons and nitrogen are cooled in a coil 76 beneath spray 84 and fed to the third stage 110. Liquid C 1 -C 3 hydrocarbons are withdrawn from stage 110 and expanded at 113 and issue from spray 86 whilst residual gas is cooled in a coil 78 beneath spray 86 and fed to the fourth stage 116 which in turn supplies liquid refrigerant to spray 88 whilst the residual gaseous methane and nitrogen is liquefied in a coil 80 beneath spray 88, expanded at 122 into a spray 90 which further cools the liquefied natural gas leaving the head of coil 52 and having itself been expanded at 54 to about 200 p.s.i.a. The product is further expanded at 58 to atmospheric pressure and fed into a storage tank 59. After being vaporized the four liquid refrigerants are recombined withdrawn through a line 124 at 41 p.s.i.a. and recycled back to compressor 94 together with make-up refrigerant mixture which together with the original charge is obtained by passing condensate from the separators 20, 34, 36 into a conventional fractionating plant 23 having flow valve controlled withdrawal lines 138, 140, 142, 144, 146 connected to a common line 126 to which is added nitrogen from an air separation plant 128.
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